Field of the Invention
The present invention relates generally to an explosive detonator device and a method for fabricating same. More specifically, the present invention relates to an improved device for generating a substantially planar shockwave for impinging upon and detonating an explosive charge, and to a method for making same.
It has long been known that the shape of the wave front used to initiate detonation of a shaped charge warhead plays a major role in determining the magnitude of explosive force jetting behavior resulting therefrom. In particular, it is known that, in theory, a planar detonation shockwave front is capable of maximizing explosive yield performance in such shaped-charge-containing warheads. Accordingly, the prior art has attempted to provide detonators capable of producing planar shockwave detonation fronts, the most successful of which will be presently detailed.
Two such prior art devices are the explosive lens and the air lens which use Baratol-containing materials and metallic flyer plate, respectively, to appropriately channel explosive force to form planar shock wave fronts. Each of these devices, however, produce shock wave fronts which require a significant amount of propagation time, and therefore, a significant amount of propagation distance (run distance), to achieve substantial planarity. This necessitates the lengthening of a warhead containing either of these two devices, so as to provide the necessary run distance (in the air lens case) within the warhead to permit the wave front generated to settle out prior to impinging upon the shaped charge liner. Thus, a warhead which incorporates either of these two devices must be longer and heavier than is desirable.
Another such prior art detonation initiator is the four-fold axisymmetric plane wave generator, which consists of a substrate with multiple, equal length grooves connected to multiple through-holes in the substrate. The multiple through-holes are grouped into four clusters centered around a common origin located at or near the center of the device. The grooves, through-holes and other void space in the substrate are filled with an explosive material. When a suitable initiation stimulus, from an electric blasting cap, is applied to the common origin, the explosive material therein detonates and the explosive force is transferred out along the grooves to the through-holes. Although this device is capable of producing a near-planar shockwave, that shockwave is subject to extremely large un-controllable pressure discontinuities along its direction of propagation. As a result, when this device is used to detonate a shaped-charged warhead the jetting performance obtained is marginal at best.
Yet another prior art detonator capable of generating a shaped shockwave is disclosed in Emerson et al, U.S. Pat. No. 4,892,039. The Emerson device comprises inner and outer conically shaped members with the outer conically shaped member having the shape of a modified frustum of a cone due to a cylindrical member extending from the smaller base of the outer conically shaped member. A space between the inner and outer conically shaped member contains an explosive material which can be discharged after ignition as a shockwave in a ring-like (annular) configuration. This device is said to produce a flatter wave front per unit length than otherwise possible, so as to be able to achieve improved explosive yield in the main charge and to permit the use of a warhead having a shorter axial length.
Unfortunately, the wave front generated by the Emerson device requires substantial propagation distance to achieve planarity. As has been described previously, this necessitates a significant increase in the axial length of the warhead and wastes warhead space that could otherwise be used to contain other features (for example, guidance electronics). Also, it has been found that the Emerson device may, under some conditions, fail to function properly. This is due to the fact that upon initiation of the explosive within the channel between the inner and outer members of the Emerson device, substantial explosive force is applied to the inner conical member. This condition may result in the collapse of the inner member, and thereby, in the failure of the device to produce the desired, substantially planar detonation wave front.
Yet another example of a prior art shaped-wave detonator is disclosed in U.S. Pat. No. 4,896,609, issued to Betts, et al.